Photocatalytic Degradation of Methylene Blue Using N-Doped ZnO/Carbon Dot (N-ZnO/CD) Nanocomposites Derived from Organic Soybean

Abstract

This study reports on successful synthesis of carbon dots (CDs), nitrogen-doped zinc oxide (N-ZnO), and N-ZnO/CD nanocomposites as photocatalysts for degradation of methylene blue. The first part was the synthesis of CDs utilizing a precursor from soybean and ethylenediamine as a dopant by a hydrothermal method. The second part was the synthesis of N-ZnO with urea as the nitrogen dopant carried out by a calcination method in a furnace at 500 °C for 2 h in an N2 atmosphere (5 °C min–1). The third part was the synthesis of N-ZnO/CD nanocomposites. The characteristics of CDs, N-ZnO, and N-ZnO/CD nanocomposites were analyzed through Fourier transform infrared (FTIR), UV–vis absorbance, photoluminescence (PL), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), thermal gravimetry analysis (TGA), field-emission scanning electron microscopy energy-dispersive spectroscopy (FESEM EDS), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET) analysis. Based on the HR-TEM analysis, the CDs had a spherical shape with an average particle size of 4.249 nm. Meanwhile, based on the XRD and HR-TEM characterization, the N-ZnO and N-ZnO/CD nanocomposites have wurtzite hexagonal structures. The materials of N-ZnO and N-ZnO/CD show increased adsorption in the visible light region and low energy gap E g. The E g values of N-ZnO and N-ZnO/CDs were found to be 2.95 and 2.81 eV, respectively, whereas the surface area (S BET) values 3.827 m2 g–1 (N-ZnO) and 3.757 m2 g–1(N-ZnO/CDs) belonged to the microporous structure. In the last part, the photocatalysts of CDs, N-ZnO, and N-ZnO/CD nanocomposites were used for degradation of MB (10 ppm) under UV-B light irradiation pH = 7.04 (neutral) for 60 min at room temperature. The N-ZnO/CD nanocomposites showed a photodegradation efficiency of 83.4% with a kinetic rate of 0.0299 min–1 higher than N-ZnO and CDs. The XRD analysis and FESEM EDS of the N-ZnO/CDs before and after three cycles confirm the stability of the photocatalyst with an MB degradation of 58.2%. These results have clearly shown that the N-ZnO/CD nanocomposites could be used as an ideal photocatalytic material for the decolorization of organic compounds in wastewater.

Organometallic one-pot synthesis of ZnO quantum dots coated by sulfoxides as L-type ligands

“…5c). The photocatalytic performance of ZnO-DMSO is relatively high compared to examples found in literature, including nanostructured ZnO thin films 87 calcined 85 or doped 88 ZnO NCs (note that direct comparison of the results may be misleading due to differences in applied both the methodologies and the character of nanomaterials, e.g. the preparation method, size of nanostructured ZnO, concentration of reagents, light source and its intensity).…”

Photocatalytic evaluation of CuO and ZnO crystallites synthesized hydrothermally using binary eugenol/iso-eugenol mixtures: isomer effects on the capping propensity of biogenic agents

“…It can be seen from Table 5 that under the experimental conditions (mimicking natural attenuation), ZnO-5 was proven to be the superior photocatalyst for the photocatalytic degradation of the studied dyes. 71–77…”

Dual Applications of Cobalt-Oxide-Grafted Carbon Quantum Dot Nanocomposite for Two Electrode Asymmetric Supercapacitors and Photocatalytic Behavior

“…On the other hand, during the oxidation process, the holes react with H 2 O to produce · OH radicals. These radicals play a crucial role in the degradation of MB, breaking down its aromatic bonds and converting it into smaller molecules such as CO 2 and H 2 O. The photodegradation process of MB in the presence of Co 3 O 4 –CQD under UV irradiation can be summarized by the following mechanism steps (eqs –). Co 3 O 4 / CQD + h ν → Co 3 O 4 false( normale − false( CB false) + normalh + false( VB false) false) / CQD false( normale − false( CB false) + normalh + false( VB false) false) Co 3 normalO 4 ( e − ( CB ) ) + CQD ( e − ( CB ) ) → ( e − ( CB ) ) + CQD ( e − ( CB ) ) + Co …”

“…On the other hand, during the oxidation process, the holes react with H 2 O to produce · OH radicals. These radicals play a crucial role in the degradation of MB, breaking down its aromatic bonds and converting it into smaller molecules such as CO 2 and H 2 O. The photodegradation process of MB in the presence of Co 3 O 4 –CQD under UV irradiation can be summarized by the following mechanism steps (eqs –). …”